1. Field of the Invention
The present invention relates to a totally enclosed motor, and more particularly, to a cooling structure of the motor.
2. Description of Related Art
FIG. 9 is a vertical cross sectional view in an axial direction of a conventional totally enclosed motor 100.
Conventionally, as shown in FIG. 9, the totally enclosed motor 100 has a structure for housing a rotor 101 and a stator 102 which generate a mechanical rotative force from electric energy, a part of a rotary shaft 103 which is connected to the rotor 101 in a unified manner and transmits the generated rotative force to outside, and a bearing 104 which supports the rotary shaft 103, inside a housing 105 consisting of a frame 105f and an end bracket 105e without disposing an opening portion.
Since the totally enclosed motor 100 has no opening portion, the totally enclosed motor 100 is prevented from entering of dusts in the air and has a sound-proof structure.
A heat of, for example, an iron loss generated in the totally enclosed motor 100 is cooled by the following mechanism shown in FIG. 10. FIG. 10 is an illustration showing a heat flow of the totally enclosed motor 100 of FIG. 9.
A heat generated in the rotor 101 is carried by heat conduction mainly in the rotary shaft 103 which is connected to the rotor 101 in a unified manner and the bearing 104 which supports the rotary shaft 103 while being supported by the housing 105, and transmitted to the housing 105. A heat generated in the stator 102 is carried to the housing 105 by heat conduction in a portion where an outer circumferential portion of the stator 102 is in contact with an inner wall of the housing 105 and by a heat transfer, for example, by heat radiation in the case when there is a clearance (gap) between the outer circumferential portion of the stator 102 and the inner wall of the housing 105.
In addition, a heat released in a space inside the housing 105 from the surfaces of the rotor 101 and the stator 102 by convection or radiation heats up air inside the housing 105. The heated up air inside the housing 105 is agitated by an inner cooling fin 106 (hereinafter, referred to as inner fin 106) which is fixed to the rotor 101 and rotates together with the rotor 101, and the heat of the heated up air is transferred to the housing 105.
An outer cooling fan 108 (hereinafter, referred to as outer fan 108) is disposed on one end side of the rotary shaft 103 in the extending direction at outside of the housing 105 in such a manner that the outer fan 108 is covered by an end fan cover 107 having a wind inlet and a wind outlet and fixed to the rotary shaft 103. The outer fan 108 generates a cooling wind flowing on a surface of a heat dissipation fin (not shown) which is formed on an outer periphery surface of the housing 105 by the rotation of the rotor 101, and the heat transferred to the housing 105 is discharged from the heat dissipation fin by the cooling wind. In this case, the end fan cover 107 has such a structure that end fan cover 107 partially covers the outer periphery of the housing 105 in the axial direction so as to guide the cooling wind toward the heat dissipation fin in order to efficiently cool the heat dissipation fin by the cooling wind of the outer fan 108 by blowing the cooling wind toward the heat dissipation fin on the housing 105. On the other hand, in the case that there is no outer fan 108, the heat transferred to the housing 105 is discharged in the atmosphere from the surface of the housing 105 by natural convection.
Meanwhile, in the inner fin 106 disposed on the rotor 101, a plate fin 106a which is formed on a surface vertical to each side of the rotary shaft 103 of the rotor 101 in the extending direction is disposed in parallel with the extending direction of the rotary shaft 103 and outward in the radial direction from the rotary shaft 103 as shown in FIG. 11 that is the rotor 101 of FIG. 9 as seen from a direction indicated by an arrow D, in consideration of molding easiness and an identical agitation performance for forward and reverse rotations of the rotor 101.
However, in the inner fin 106 of this structure, since a turbulent flow occurs around the center side of the fin 106a of the inner fin 106, while a cooling effect is obtained by blowing air outward from the center side of the inner fin 106 by the centrifugal force and agitating air inside the housing 105, the cooling efficiency is not good by disturbance of a laminar flow flowing outward from the center side of the inner fin 106 by the turbulent flow.
FIG. 12 is a vertical cross sectional view showing an air flow around the inner fin 106 of the conventional totally enclosed motor 100 of FIG. 9 by arrows.
As shown by the arrows in FIG. 12, air agitated by the inner fin 106 only circulates around the inner fin 106, and it was demonstrated that a wind velocity between the housing 105 and around coil end 109 was extremely decreased. Therefore, a space inside the housing 105 is not cooled homogeneously.
In addition, in a small gap between the rotor 101 and the stator 102, there is really a very little wind flow between a load side 110 where a motor load is disposed at end portions of the rotor 101 and the stator 102 in the axial direction (a right-left direction in FIG. 12) inside the housing 105 and a no-load side 111. Then, the inner fin 106 agitates air in a space on the load side 110 inside the housing 105 and air in a space on the no-load side 111, independently. As a result, only a local cooling effect is obtained, and an efficient cooling can not be achieved.
Regarding the structure of the inner fin 106, in order to improve the cooling performance, Japanese Patent Publication No. S58-207849 (see, for example, FIG. 1) proposed the following method that as shown in FIG. 13 that is a vertical cross sectional view of a rotor 201 in the axial direction, in the rotor 201 of a squirrel-cage motor with an end ring 212, a conductor 213 which is located on the outer side than the end ring 212 and inserted into the rotor 201 so as to pass through the rotor 201 in the direction of the rotary shaft 203 is disposed to be inclined in a direction opposite to a rotation direction 214. As a result, according to the method, an agitation power of a space inside the motor is increased by the rotation of the conductor 213 located on the outer side than the end ring 212.
In addition, in a totally enclosed motor 300 of Japanese Utility Model Publication No. S61-43765 (see, for example, FIG. 1), the following method is disclosed, in which wind holes 351, 352 are disposed in a rotor 301 and a stator 302, respectively, and air inside a housing 305 is forcibly circulated by an inner cooling fan 316 (hereinafter, referred to as inner fan 316) disposed inside the totally enclosed motor 300 and connected to a rotary shaft 303, as shown in FIG. 15 that is a vertical cross sectional view in the axial direction of the totally enclosed motor 300.